SEMICONDUCTOR RADIATION WAVELENGTH DETECTOR
 Inventors: Charles R. Layne, Orlando; M.
William Ford, Maitland, both of Fla.
 Assignee: Martin Marietta Corporation, New York, N.Y.
 Filed: Sept. 23, 1975
 Appl. No.: 616,115
Related U.S. Application Data
 Continuation of Ser. No. 465,652, April 30, 1974, abandoned.
 U.S. CI 356/195; 250/211 J;
 Int. CI.2 G01J 3/46; H01J 39/12;
 Field of Search 357/58, 30; 250/211 J,
250/226, 214 R; 356/229, 173, 195
 References Cited
UNITED STATES PATENTS
3,304,430 2/1967 Biard et al 250/211 J
3,478,214 11/1969 Dillman 250/211 J
3,484,663 12/1969 Halus 250/211 J
Primary Examiner—Alfred E. Smith
Assistant Examiner—T. N. Grigsby
Attorney, Agent, or Firm—Sughrue, Rothwell, Mion,
Zinn & Macpeak
A double-layer photodiode is created in an integral
structure to form two diodes, the upper diode having a relatively thin active region and the lower diode a relatively thick active region. Light whose wavelength is to be measured is directed onto the upper diode. The thickness of the first diode is chosen so that, in the spectrum of light wavelengths being measured, the energy of the shortest wavelength is entirely absorbed therein. As the radiation wavelength increases, the absorption by the upper diode decreases exponentially, and the unabsorbed light is transmitted through the thin active region into the thick active region of the lower diode where it is absorbed. The thickness of the active region of the lower diode is chosen so that it absorbs substantially all of the energy of .longest wavelength in the spectrum being measured. The absorption of the photon energy in each diode creates electronhole pairs therein which produce in each diode a change in conductivity which is proportional to the absorbed energy. Therefore, since the difference in conductivities of the two diodes is a function of the wavelength of the incident light, as the wavelength changes, the difference between changes in the conductivity of the two diodes, divided by the sum of the changes in conductivity, is a function which is a singlevalued function of the wavelength of the incident light and which is independent of the intensity of the incident light. A measuring circuit connected to the double-layer diode provides a direct reading of the wavelength. Furthermore, there is disclosed a method for fabricating a double-layer- photodiode suitable for use in the wavelength detector.
10 Claims, 7 Drawing Figures